Sensor identification method and system

ABSTRACT

An inventive method and system are provided for identifying a compatible photoplethysmographic sensor when interconnected to a given photoplethysmographic monitor. The method and system may further provide for the identification of which of a plurality of compatible sensors is interconnected to allow for selective calibration of the photoplethysmographic monitor. In this regard, the system and method may entail provision of a predetermined drive or test signal to a light source and/or identification element (i.e., sensor elements) of a photoplethysmographic sensor, and the obtainment of a corresponding output signal for use in sensor identification. In one approach, an output signal is obtained from at least one of three sensor elements each of which is interconnected between a different pair of sensor terminals which is a unique combination of two of four sensor terminals on the sensor. In this regard, individual circuits may be formed through each sensor element allowing for enhanced flexibility in signal application.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. 119(e)(1) toU.S. Provisional Application No. 60/353,471 entitled: “SensorIdentification Method and System,” filed on Jan. 31, 2002; the contentsof which are incorporated herein as if set forth in full.

FIELD OF THE INVENTION

[0002] The present invention relates to the field ofphotoplethysmography, and more specifically, to an improved method andsystem for identifying a photoplethysmographic sensor selectivelyinterconnectable to a photoplethysmographic monitor, e.g. to confirmcompatibility with and/or otherwise “calibrate” the monitor for accuratemeasurements. The invention is particularly apt for pulse oximetryapplications.

BACKGROUND OF THE INVENTION

[0003] In the field of photoplethysmography light corresponding with twoor more different centered wavelengths may be employed to non-invasivelydetermine various blood analyte concentrations. For example, bloodoxygen saturation (SpO₂) levels of a patient's blood may be monitored inpulse oximetry systems by measuring the absorption of oxyhemoglobin andreduced hemoglobin using red and infrared light. The measured absorptiondata allows for the determination of the relative concentration ofreduced hemoglobin and oxyhemoglobin, and therefore SpO₂ levels, sincereduced hemoglobin absorbs more light than oxyhemoglobin in the red bandand oxyhemoglobin absorbs more light than reduced hemoglobin in theinfrared band; and since the absorption relationships of the twoanalytes in the red and infrared bands are known. See e.g., U.S. Pat.Nos. 5,934,277 and 5,842,979.

[0004] As may be appreciated, in order to accurately compute bloodanalyte concentrations, it is important for pulse oximetry systems to bepreset, or “calibrated”, in relation to the center wavelengths of redand infrared light employed. In this regard, pulse oximetry arrangementstypically comprise a disposable or reusable sensor that is releasablyattached to a given patient's appendage (e.g., finger, ear lobe, infantfoot or nasal septum) for a given patient monitoring procedure. Thesensor carries at least one red light source and one infrared lightsource, as well a light detector to provide an output signal indicativeof the light received thereby (e.g. the red and infrared light passingthrough the patient appendage). In turn, the sensor may be connected orselectively interconnectable to a cable that is selectivelyinterconnectable to a photoplethysmographic monitor to process thedetector output signals.

[0005] Given such selective interconnections, a number of approacheshave been developed for identifying a given sensor to an interconnectedphotoplethysmographic monitor so as to insure compatibility (e.g. sothat the monitor may process the sensor detector output signal basedupon assumed or calibrated values, or algorithms, reflective of thecenter wavelength(s) of the interconnected sensor light source(s)). Suchknown approaches largely entail the utilization of dedicated sensorcomponentry and corresponding cable connections, thereby adding cost,complexity and mass. Further, many of the known approaches raisereliability concerns since the identifying componentry can be easilyimplemented by sensor suppliers offering sensors that do not otherwisesatisfy performance parameters established for accurate measurements byand/or effective use of a given interconnectable monitor.

SUMMARY OF THE INVENTION

[0006] A general objective of the present invention is to provide animproved approach for photoplethysmographic sensor identification.

[0007] A more specific objective of the present invention is to providefor photoplethysmographic sensor identification in a manner that doesnot require dedicated sensor componentry or increased complexity.

[0008] Yet a further objective of the present invention is to providefor improved photoplethysmographic sensor identification in a mannerthat facilitates enhanced reliability and/or otherwise allows forincreased identification capabilities.

[0009] One or more of the above objectives and additional advantages arerealized by the present invention which provides for the identificationof compatible/incompatible photoplethysmographic sensors by a givenphotoplethysmographic monitor interconnected thereto. To realize suchbenefits, the present inventor has recognized that the light source(s)and/or light detector(s) employed in photoplethysmographic sensors haveunique and predeterminable operating characteristics. Therefore, apredetermined drive, or interrogation test, signal can be provided to agiven sensor interconnected to a given monitor to yield a “testsignature” that can be used to identify the sensor, e.g. via comparisonto one or more “reference signatures” pre-established in relation to oneor more sensors known to be compatible with the monitor.

[0010] The inventive method and system entail: (i.) the provision of apredetermined drive signal to the light source(s) of a givenphotoplethysmographic sensor, (ii.) the obtainment of at least one of anoutput signal from a light detector comprising the sensor (e.g. which isindicative of light received thereby) and an output signal from thelight source(s) and/or an associated identification element (e.g. whichis indicative of any signal passing therethrough), and (iii) theutilization of the output signal to identify the photoplethysmographicsensor. As may be appreciated the predetermined drive signal and theoutput signal may be provided and processed, respectively, by aphotoplethysmographic monitor to which a given photoplethysmographicsensor has been selectively interconnected. Such monitor may compare thetest signature obtained via processing to one or more stored referencesignatures that correspond with known compatible sensors.

[0011] Sensor “identification” confirms that a given sensor iscompatible for use with an interconnected photoplethysmographic monitor.In turn, for example, the monitor may be enabled to make“photoplethysmographic measurements” utilizing the interconnectedsensor. Alternatively, if compatibility is not confirmed, the monitormay be totally or partially disabled, e.g. to “lock-out” use of thesensor with the monitor for all or at least certain“photoplethysmographic measurement” functionalities. For purposeshereof, “photoplethysmographic measurements” may entail blood analytedeterminations, including in particular blood oxygen saturation values,as well as pulse/heart rate, and other related determinations. Inconjunction with sensor identification, the inventive method and systemmay provide for an identification of which of a plurality of compatiblesensors is interconnected to a monitor. A sensor detector output signalmay then be processed using stored selected/calibrated values, oralgorithms, corresponding with the identified sensor, forphotoplethysmographic measurements.

[0012] In one sensor identification approach, a sensor light detectoroutput signal may be utilized to yield a test signature that simplyindicates whether a light source(s) of an interconnected sensor emitslight in response to a predetermined drive signal. Further, the testsignature may indicate when such emission(s) is evidenced in the lightdetector output signal in response to the predetermined drive signal. Inthis regard, it should be appreciated that, for any givenphotoplethysmographic sensor, the illumination response of thecorresponding light source(s) (e.g. the capability and/or time delay toemit light) and the output signal response of the corresponding lightdetector (e.g. the time delay and wavelength sensitivity for signalresponse) may be predetermined for a given predetermined drive signal,i.e. to establish a reference signature. In connection with thisapproach, the method may further provide for the use of a predetermineddrive signal whose magnitude (e.g. voltage/current) is varied in apredetermined manner. This approach yields a test signature comprisingone or more portions per source, wherein each portion indicates whethera given source was on or off during each of one or more correspondingtime periods. In turn, the test signature portions may be compared tocorresponding portions of one or more reference signature(s) of knowncompatible sensors for a given monitor.

[0013] To identify a compatible sensor(s) having a plurality of lightsources, a corresponding reference signature(s) may be established whichis indicative of whether two or more of the light sources emit light inresponse to corresponding portions of a predetermined drive signal (e.g.such portions applying the same or different signal magnitude levels tothe sources). Such reference signature(s) may be stored at a givenphotoplethysmographic monitor and compared with a corresponding testsignature obtained from a given interconnected sensor to be identified.As will be appreciated, the use of plural light sources for sensoridentification provides added information to the test signature andreference signature(s), thereby enhancing the identification process.

[0014] In another sensor signature identification approach, a detectoroutput signal may be utilized to yield a test signature that indicatesthe intensity of light emitted by the light source(s), as detected bythe detector, of an interconnected sensor in response to a predetermineddrive signal. Further, the test signature may indicate when such lightintensity is evidenced by the light detector output signal in responseto the predetermined drive signal. In conjunction with this approach, itshould be appreciated that, for a given photoplethysmographic sensor,the light source(s) utilized therein will have a predeterminable,corresponding emission intensity-to-time function (e.g. for rampingup/down), and the light detector utilized therein will have apredeterminable output response (e.g. a time delay for and wavelengthsensitivity of signal response), for a given predetermined drive signal.As such, the invention may provide for a determination of whether thelight source(s) emits radiation and light detector detects radiation inaccordance with one or more predetermined intensity-to-time functionsestablished in relation to one or more known, compatible sensors. Inthat regard, this approach yields a test signature comprising one ormore intensity indication portions per light source that may be comparedto corresponding portions of one or more reference signature(s) of knowncompatible sensors stored by a given monitor. In connection with thisapproach, the method may again provide for the use of a predetermineddrive signal whose magnitude (e.g. voltage/current) is varied in apredetermined manner.

[0015] When a photoplethysmographic sensor includes a plurality of lightsources the detector output signal may be utilized to determine whethertwo or more of the light sources emit radiation within correspondingpredetermined intensity ranges, as detected by the light detector, inresponse to the predetermined drive signal. Further determinations canalso be made as to whether the two light sources emit radiation that isdetected in accordance with corresponding, predeterminedintensity-to-time functions.

[0016] In making the foregoing determinations regarding the intensity oflight source emissions, at least one test signature value may beobtained in an identification procedure which is indicative of a ratiobetween a current applied to a sensor light source(s) and the measureddetector output current. In turn, the test signature value(s) may becompared to pre-established reference signature values correspondingwith like ratios for known, compatible sensors when a like drive signalis applied thereto. The utilization of “current ratios” may provide anumber of advantages, e.g. cancellation of signal noise components.

[0017] In conjunction with the above-noted approaches it may be notedthat, since a detector output signal is utilized for sensoridentification, a sensor under test should be provided or otherwiseoriented so that the light source(s) and light detector thereof are inat least partial alignment. Further, to facilitate sensoridentification, either prior to or after positioning on a patientappendage, the invention may utilize preprogrammed functionality thatutilizes a sensor detector output signal to automatically determinewhether the interconnected sensor has been attached to a patient (e.g.via comparisons to predetermined thresholds), then utilizescorresponding predetermined reference signatures of known compatiblesensors for identification. That is, different reference signature setsmay be selected in relation to the determination of whether the sensorunder test is attached or unattached to a patient.

[0018] In yet another sensor identification approach, an output signalfrom an interconnected sensor light source(s) (e.g. which is indicativewith any signal passing therethrough) may be utilized to yield a testsignature which indicates whether the light source(s) emits light inresponse to a predetermined drive signal, and if so, a magnitude of theoutput signal. In the later regard, it should be appreciated that, e.g.for any given photoplethysmographic sensor, the voltage drop across thecorresponding light source(s) may be predetermined for a givenpredetermined drive signal, i.e. to establish a reference signature thatmay be compared to a test signature for identification.

[0019] In connection with this approach, the invention may furtherprovide for the use of a predetermined drive signal whose magnitude(e.g. current/voltages) and/or polarity is varied in a predeterminedmanner. In the former regard, it should be appreciated that, e.g. forany given sensor the magnitude of voltage drop across the correspondinglight source(s) has a predeterminable relationship to the magnitude ofthe current passing through the light source(s) and that suchrelationship may be non-linear. As such, distinct reference signaturesmay be established/utilized that comprise a plurality of portionscorresponding with each light source (e.g. each portion corresponding toa different drive signal magnitude).

[0020] As to the variation of drive signal polarity, it may beappreciated that, for sensors utilizing a diode light source(s), thepolarity of the predetermined drive signal determines the operability ofthe diode light source(s). That is, the drive signal may be selectivelyforward-biased and reverse biased, wherein the magnitude of the diodelight source(s) output signal will be substantially zero whenreverse-biased. Such biasing yields further test and reference signatureinformation for sensor identification.

[0021] Of note, the utilization of a light source(s) output signal forsensor identification may be advantageous in that the light source(s)and detector of a sensor need not be aligned for sensor identification.As such, the identification procedure may be completed either prior toor after attachment to a patient.

[0022] To further enhance the accuracy and reliability of the variousapproaches noted above, the predetermined drive signal may be providedfor a number of cycles to obtain a corresponding number of testsignatures. For example, where a predetermined voltage is sequentiallyapplied for n cycles to m source(s) comprising a given interconnectedsensor, n test signatures may be obtained from the output signal,wherein each of the test signatures includes at least m signatureportions. In turn, corresponding portions of the test signatures may bestatistically processed to enhance the accuracy of identification. Suchprocessing may entail the computation of average, median, range and/orstandard deviation values that are employable in comparing andpotentially matching test signatures to reference signatures. In thatregard, it should also be noted that two or all of the variousapproaches noted above can be utilized in combination to further enhancethe accuracy of sensor identification.

[0023] When the photoplethysmographic sensor to be identified includes aplurality of light sources (e.g. with a single detector), thepredetermined drive signal utilized for sensor identification mayprovide for pulsing of such light sources in accordance with apredetermined multiplexing scheme. Further, the utilization of thedetector output signal may entail demultiplexing of the signal incorresponding relation to the predetermined multiplexing scheme. Thepredetermined multiplexing/demultiplexing schemes may be any of severalknown in the art, including one selected from a group consisting of timedivision multiplexing, frequency division multiplexing and code divisionmultiplexing. Any of these schemes facilitate the separate processing ofdetector output signal portions that correspond with the different lightsources present in the sensor to be identified.

[0024] In yet a further aspect of the invention, the present inventionmay further provide for the conversion of an analog output signal fromthe detector and/or light source(s) into digital form for digitalprocessing. Such conversion may preferably provide for data sampling ata rate which is at least two times greater than the greatest modulationfrequency applied to the light source(s).

[0025] In an additional aspect, the invention may be employed toidentify sensors having at least two light sources and a light detector,wherein when interconnected to a compatible monitor at least one of thelight sources is only utilized for sensor identification purposes (e.g.such light source is not utilized for photoplethysmographicmeasurements).

[0026] By way of primary example, in certain current applications aphotoplethysmographic sensor having three light sources and a detectoris employable with two different types of photoplethysmographicmonitors. When interconnected with a first type of photoplethysmographicmonitor, first and second ones of the sensor light sources are utilizedfor photoplethysmographic measurements (e.g. a first infrared lightsource and a first red light source). When interconnected to a secondtype of photoplethysmographic monitor, first and third ones of thesensor light sources are employed for photoplethysmographic measurements(e.g. the first infrared light source and a second red light source).

[0027] The invention may be employed with either the first and/or secondtype of photoplethysmographic monitors. For example, when the sensor isinterconnected to the first type of monitor the third light source willonly be utilized by the monitor for sensor identification purposes. Suchan arrangement advantageously makes use of the “extra” light source(e.g. not otherwise employed for photoplethysmographic measurements inone of the alternative applications) for sensor identification purposes.

[0028] According to a general series of embodiments, an inventivephotoplethysmographic system includes a photoplethysmographic sensorhaving first and second light sources and an identification element(e.g. a third light source). These light sources and identificationelement are electrically interconnected between four terminals on thesensor. In this regard, each sensor element (e.g. each light source oridentification element) is interconnected between a different pair ofsensor terminals (i.e. each different pair of sensor terminals comprisesa unique combination of two of the four sensor terminals). Statedanother way, none of the sensor elements are in a parallel relationshipwith another sensor element and each pair of terminals shares at leastone terminal with another sensor terminal pair.

[0029] The system also includes a photoplethysmographic monitorreleaseably interconnected to each of the first, second, and thirdsensor terminal pairs. For example, the monitor may be selectivelyinterconnected to the sensor using a cable, wherein the cable itself maybe connected or selectively interconnectable to the sensor. The monitoris operative to selectively apply predetermined signals to one of theterminals of each of the three sensor terminal pairs in order to obtainoutput signals at a second terminal of each of those pairs. Moreparticularly, the monitor is operable to selectively apply drive and/orinterrogation signals to each of the sensor elements. In turn, themonitor is operable to obtain an output signal(s) at a second terminalof one or more of the terminal pairs in response to the interrogationand/or drive signals. One or more of these output signals may beutilized by a processor operatively associated with the monitor toidentify the sensor interconnected to the monitor. For example, theoutputs signal(s) may be processed to produce one or more testsignature(s) for comparison with one or more stored referencesignature(s). As may be appreciated, if the output signal(s) and/or testsignature(s) does not correspond to a value(s) associated with knownsensors, the monitor may be disabled.

[0030] In typical arrangements the monitor may be operative to applyinterrogation and/or drive signals of varying magnitudes and/orpolarities to the sensor terminals. For example, drive signals may beprovided to selectively pulse the light sources duringphotoplethysmographic monitoring. In turn, for monitoring purposes, thesensor will further include a light detector for providing an outputsignal indicative of the light from the light sources as attenuated bypatient tissue.

[0031] While the monitor is operable to apply interrogation and/or drivesignals across any of the sensor elements, in a given system arrangementthe identification element will typically be utilized only to provide anoutput signal for identification purposes. In one embodiment, theidentification element may comprise a diode. In this regard, the firstand second light sources as well as the identification element may eachcomprise light emitting diodes. As may be appreciated, in typicalapplications the use of a simple diode identification element will yieldan output signal that reflects a minimal and predeterminable voltagedrop across the corresponding terminal pair in response to an appliedinterrogation signal. Accordingly, this voltage drop output signal maybe utilized for sensor identification purposes.

[0032] In order to apply individual interrogation and/or drive signalsto any of the sensor elements, the sensor terminals may beinterconnected to the monitor via dedicated electrical pathways. In thisregard, individual circuits may be formed through any of the sensorelements allowing the monitor to independently apply signals to adesired sensor element. Furthermore, these individual circuits allow forswitching the polarity of an interrogation signal as applied to a givensensor element.

[0033] In a sensor identification approach applicable with thephotoplethysmographic system utilizing the four-terminal, three-sensorelement sensor configuration, one or more interrogation signals areapplied across a pair of terminals associated with the identificationelement and/or light sources in order to obtain one or more outputsignal(s). In turn, the output signal(s) may be employed for sensoridentification.

[0034] Applying a drive or interrogation signal across a given pair ofterminals comprises applying a signal to a first terminal of theterminal pairs in order to obtain an output signal at the secondterminal. In this regard, the signal applied to the first terminal maypass through the sensor element between the terminals. Accordingly, fora “known” sensor, the output signal at the second terminal may bepredeterminably about the same or different from the input signal. Forexample, for a forward-biased, light emitting diode the output signalmay reflect a minimal, yet predeterminable voltage drop relative to theinput signal. On the other hand, for a reverse-biased, light emittingdiode, the output signal may predeterminably indicate the absence of anysignal passing through light emitting diode. Applying an interrogationsignal to other types of identification element(s) (e.g. resistor(s))may cause a predeterminable and relatively significant voltage dropand/or change in current between the first and second sensor terminals.In any case, the comparison of an output signal with a predeterminedvalue may be utilized for sensor identification. As may be appreciated,in addition to applying an interrogation signal(s) to the identificationelement, one or more interrogation signals may be applied to the lightsources to produce additional output signals. These additional outputsignals may be used separately or in combination with output signalsfrom the identification element for sensor identification and/or monitorcalibration purposes.

[0035] In one embodiment, an interrogation signal may be applied acrossthe identification element and/or light sources in a manner thatproduces at least two output signals. In this regard, more accurate testsignatures may be produced for sensor identification. Obtaining twooutput signals from a sensor element interconnected between a pair ofterminals may require applying first and second interrogation signals oraltering the polarity of a single interrogation signal as applied to theterminals.

[0036] In one embodiment, the magnitude of first and secondinterrogation signals, as applied to the identification element, isvaried in order to produce two output signals. That is, the currentlevel and/or voltage of the interrogation signal is varied between firstand second signals in order to produce first and second output signals.For example, when the identification element is a light emitting diode,first and second interrogation signals having first and second currentlevels may be applied across the diode's sensor terminals. As may beappreciated, a voltage drop associated with each interrogation signalmay be recorded as first and second output signals. The light emittingdiode is selected such that first and second interrogation signalshaving first and second different current levels produce minimal andsubstantially equal voltage drops (i.e., output signals). In thisregard, two predeterminable and substantially identical output signalsmay be produced in response to two different interrogation signals.

[0037] Once the output signals are utilized to identify the sensor, thephotoplethysmographic monitor may be utilized to apply drive signals tothe first and second light sources as well as a light detector in orderto perform plethysmographic monitoring. In order to prevent crosstalk orother contamination from the identification element, which may be alight emitting diode, the circuit interconnected to the informationelement may be disabled prior to monitoring. In any case, the monitor isoperable to provide drive signals to the light sources and detector inorder to pulsate light through tissue-under-test as well as obtain anoutput signal indicative of that pulsating light as attenuated by saidtissue.

[0038] Numerous additional aspects and advantages will be apparent tothose skilled in the art upon review of the further description thatfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIGS. 1A and 1B illustrate alternate embodiments ofphotoplethysmographic system applications of the present invention.

[0040]FIGS. 2A and 2B illustrate sensor, cable and monitorinterconnections for the applications of FIGS. 1A and 1B.

[0041]FIG. 3 illustrates an automated sensor identification procedurewhich implements the present invention.

[0042]FIG. 4 illustrates a further embodiment of a sensor, cable andmonitor.

[0043]FIG. 5 illustrates an automated sensor identification procedureutilized with the system of FIG. 4.

DETAILED DESCRIPTION

[0044]FIGS. 1A, 2A and 1B, 2B illustrate two alternatephotoplethysmographic system applications of the present invention. Theillustrated systems may each identify and selectively employ compatiblesensors, including sensors that are compatible with each of the systems.In the later regard, the invention is no way limited to dualcompatibility implementations.

[0045] In the application of FIG. 1A, a first photoplethysmographicmonitor 20 a is shown interconnected to an interconnectable sensor 10via a first type of cable 30 a, while in the application of FIG. 1B asecond photoplethysmographic monitor 20 b is shown interconnected to theinterconnectable sensor 10 by a second type of cable 30 b. For purposesof the present description, sensor 10 is of a type that is compatiblewith either of the monitors 20 a, 20 b. The first and secondphotoplethysmographic monitors 20 a, 20 b may vary in type, however,including differing electrical configurations of their respective cableinterconnection ports 22 a, 22 b and corresponding internalphotoplethysmographic measurement features.

[0046] By way of example, monitor 20 a may be designed with port 22 aincluding two electrical pins or sockets for driving two light sourcesof a photoplethysmographic sensor. On the other hand, monitor 20 b maybe designed with port 22 b including three electrical pins or socketsfor driving two or more light sources of a photoplethysmographic sensor.

[0047] In the system applications shown in FIGS. 1A and 1B,photoplethysmographic monitors 20 a, 20 b comprise processors 21 a, 21 band clocks 26 a, 26 b that may operate to trigger light source drives 22a, 22 b to transmit drive signals via cables 30 a, 30 b to aninterconnected sensor (e.g. the interconnectable sensor 10). Moreparticularly, since sensor 10 is compatible in the illustratedapplications, a drive signal may be provided in each application topulse the light sources 12, 14 and/or 16 in accordance with apredetermined multiplexing scheme (e.g. a time-division,frequency-division or code-division multiplexing scheme) causing sources12, 14 and/or 16 to emit light at different, correspondingcentered-wavelengths for which monitors 20 a, 20 b have been preset ormay be calibrated for operation.

[0048] By way of example, for normal photoplethysmographic measurements,in the system application of FIG. 1A light sources 12 and 14 may beselectively pulsed to illuminate a patient tissue under test (e.g. withred and infrared light at first and second centered wavelengths,respectively). In the system application of FIG. 1B light sources 12 and16 may be selectively pulsed to illuminate a patient tissue under test(e.g. with red and infrared light at first and third centeredwavelengths, respectively). Upon tissue illumination, a light detector18 comprising sensor 10 may detect the intensity of light transmitted bythe tissue under test and provide a corresponding output signal. Inturn, monitors 20 a, 20 b may process the detector output signalutilizing stored values, or algorithms preset in relation to thecenter-wavelengths of the light sources 12, 14 and/or 16 of sensor 10.Of note, and as will be further described, the light sources 12, 14and/or 16 are also employed in the illustrated applications for sensoridentification purposes.

[0049] In the system applications of FIGS. 1A and 1B, the detectoroutput signal of sensor 10 may be transmitted by cables 30 a, 30 b forconversion/conditioning by detection circuits 23 a, 23 b, and processingby processors 21 a, 21 b comprising monitors 20 a, 20 b, respectively.For example, detection circuits 23 a, 23 b may comprise amplificationand analog-to-digital conversion componentry. If employed, theanalog-to-digital componentry should preferably sample the detectorsignal at a rate which is at least two times the greatest frequency usedfor light source for multiplexing. Detection circuits 23 a, 23 b orprocessors 21 a, 21 b also may be provided to demultiplex detectorsignals (e.g. in corresponding relation to a given light sourcemultiplexing scheme) so that signal portions corresponding with thelight sources 12, 14 and/or 16 may be separately processed.

[0050] In conjunction with such processing, sensor 10 may be initiallyidentified to confirm compatibility. Then, one or morephotoplethysmographic measurements may be determined using the detectoroutput signal and output to a user via monitor displays 24 a, 24 b. Byway of example, the first and second photoplethysmographic monitors 20a, 20 b may utilize the detector output signal to determine SpO₂ andpulse/heart rate values. Monitors 20 a, 20 b may each further include auser control panel 25 a, 25 b to allow for user control and overrideoptions as will be further described.

[0051] Referring now to FIGS. 2A and 2B, it can be seen that the lightsources 12, 14 and 16 of sensor 10 may be electrically interconnectedbetween sensor terminals 62 and 64, 60 and 64, and 60 and 66,respectively. In use of the FIG. 2A arrangement, either or both of lightsources 12 and 14 may be utilized for identification purposes andphotoplethysmographic measurements. For purposes of driving light source12, clock 26 a, processor 22 a and drive source 26 a of monitor 20 a maycause a negative charge to be applied to sensor terminal 62 and apositive charge to be applied to sensor terminal 64 via cable connectionlines 80 and 82, respectively. Selective driving of light source 14 maybe provided by the selective application of a negative charge to sensorterminal 64 and positive charge to sensor terminal 60 via cableconnection lines 82 and 80, respectively. As may be noted, the cableconnection line 80 includes first and second spurs 80 a and 80 b forinterconnection with sensor terminals 60 and 62, respectively, therebyfacilitating an arrangement in which cable 30 a presents a two terminalconnection (i.e., via cable connection lines 80 and 82) to the port 22 aof the first type of photoplethysmographic monitor 20 a. To detect lightsignals transmitted by the tissue under test, processor 22 a of monitor20 a may cause a negative charge to be applied to sensor terminal 56while applying a positive charge to sensor terminal 58. As will beunderstood, such detection may be coordinated with the driving of lightsources 12 and 14.

[0052] In use of the FIG. 2B arrangement, any or all of the lightsources 12, 14 and 16 may be utilized for identification purposes, whileonly light sources 12 and 16 are utilized for photoplethysmographicmeasurements. For purposes of driving light source 12, clock 26 b,processor 21 b and drive source 22 b of monitor 20 b may cause anegative charge to be applied to sensor terminal 62 and a positivecharge to sensor terminal 64 via cable connection lines 94 and 96,respectively. Light source 14 may be driven by applying a negativecharge to sensor terminal 64 and a positive charge to terminal 60.Driving of light source 16 may be provided by application of a negativecharge to sensor terminal 60 and a positive charge to sensor terminal 66via cable connection lines 92 and 96, respectively. As may be noted,cable connection line 96 includes first and second spurs 96 a and 96 bfor interconnection with sensor terminals 64 and 66, respectively,thereby facilitating an arrangement in which cable 20 b presents a threeterminal connection (e.g., via cable connection lines 92, 94 and 96) tothe port 22 b of monitor 20 b. To detect light signals transmitted bythe tissue under test, processor 22 b of monitor 20 b may cause anegative charge to be applied to sensor terminal 56 while applying apositive charge to sensor terminal 58. As will be understood, suchdetection may be coordinated with the driving of the light sources 12,14 and/or 16. Re

[0053] turning now to FIGS. 1A and 1B, processor unit 20 a, 20 b maycomprise one or more data storage buffers to store detector outputsignal data values received from detector circuit 23 a, 23 b, as well asadditional values computed by various computation modules comprisingprocessor 20. In the latter regard, such computation modules may includea sensor identification module 40 a, 40 b for use in conjunction withthe present invention, a blood analyte measurement module 28 a, 28 b forproviding blood analyte information (e.g., blood oxygen saturationvalues), and other modules for providing other photoplethysmographicmeasurement information derivable from the data stored at the processorbuffer(s).

[0054] In the later regard, blood analyte measurement module 28 a, 28 bmay access buffer data values to compute differential absorption datasets (e.g., differential infrared light and differential red light datasets) from which blood analyte values may be determined utilizing storedvalues, or algorithms, which are based upon the center-wavelengths ofthe light sources of a given compatible sensor, e.g. light sources 12,14, 16 of the interconnectable sensor 10. In this regard, blood analytecomputation measurement modules 28 a, 28 b may incorporate known processfunctionalities, including those taught by U.S. Pat. Nos. 5,503,148;5,842,979; 5,891,024 and 5,934,277.

[0055] As noted, sensor identification modules 40 a, 40 b, provide forthe identification of compatible, interconnected sensors. Moreparticularly, sensor identification module 40 a, 40 b may be provided tocause light source drives 22 a, 22 b to apply a predetermined drivesignal, or interrogation test signal, to an interconnected sensor, andto process detector output signal data obtained from the interconnectedsensor via detector circuit 23 a, 23 b to determine if theinterconnected sensor is compatible.

[0056] In one identification approach, sensor identification modules 40a, 40 b may process detector signal data to determine whether one ormore light sources of an interconnected sensor (e.g. sensor 10) emitradiation in response to a interrogation test signal provided by lightsource drives 22 a, 22 b. More particularly, the detector signal datamay be processed to determine whether a given interconnected sensoremits radiation within one or a plurality of different time periods inresponse to the drive signal. In this regard, the sensor identificationmodules 40 a, 40 b may utilize preset values, or algorithms, indicativeof the illumination response(s) of light source(s) comprising one ormore known, compatible sensor(s) when driven by a predetermined drivesignal. That is, the “test signature” defined by the detector signaldata may be compared with a “reference signature” defined by storedillumination response values or algorithms, to identify theinterconnected sensor.

[0057] By way of example, in the system application corresponding withFIGS. 1B and 2B, light sources 12, 14 and 16 may be pulsed one or morecycles in accordance with a predetermined multiplexing scheme. In turn,the detector signal data may be demultiplexed to yield detector signaldata portions in corresponding relation to the pulsing of sources 12, 14and 16. Such portions may then be processed in relation to (e.g.compared to) stored values, or algorithms, pre-established incorresponding relation to the light sources of one or more known,compatible sensors, including sensor 10. In turn, stored look-up valuesor algorithms (e.g. based on the center-wavelengths of the sources insensor 10 may be selected/calibrated for use in photoplethysmographicmeasurements.

[0058] In another identification approach, the sensor identificationmodules 40 a, 40 b may process the detector output signal data todetermine whether one or more light sources of an interconnected sensor(e.g. sensor 10) emit light within a predetermined intensity range inresponse to a interrogation test signal provided by light source drives22 a, 22 b. More particularly, the detector signal data may be processedto determine whether a given interconnected sensor emits light inaccordance with at least one predetermined stored intensity-to-timefunction. In this regard, the sensor identification modules 40 a, 40 bmay utilize preset values, or algorithms, indicative of theintensity-to-time function(s) corresponding with the light source(s) ofone or more known, compatible sensor(s) when driven by a predeterminedsignal. Again, the “test signature” defined by the detector signal datamay be compared with a “reference signature” defined by storedintensity-to-time function values, or algorithms, to identify theinterconnected sensor.

[0059] By way of example, in the system application corresponding withFIGS. 1A and 1B, light sources 12 and 14 may be pulsed one or morecycles in accordance with a predetermined multiplexing scheme. In turn,the detector signal data may be demultiplexed to yield detector signaldata portions in corresponding relation to the pulsing of sources 12 and14. Such portions may then be processed in relation to (e.g. comparedto) stored values or algorithms preset corresponding relation to thelight sources of known, compatible sensors. Such processing confirmscompatibility, and where the intensity-to-time attributes of pluralknown, compatible sensors are stored by monitors 40 a, 40 b, allows forthe identification of a particular interconnected, compatible sensor,including sensor 10. Again, appropriate stored look-up values, oralgorithms (e.g. based on the center-wavelengths of the light sources insensor 10) may be selected/calibrated for use in photoplethysmographicmeasurements.

[0060] In yet another identification approach, the sensor identificationmodules 40 a, 40 b may process signal data obtained from output signals,or signals passing through, light sources 12, 14 and/or 16 in responseto a interrogation test signal(s) applied thereto. For example,processing of such signal data may provide a “test signature” indicativeof the voltage drop(s) across one or more of the light sources 12, 14and/or 16 in response to a test interrogation signal comprising one ormore magnitudes. Again comparison with corresponding “referencesignatures” yields sensor identification. Utilization of interrogationsignals as applied to one or more light sources will be more fullydiscussed below in relation to FIGS. 4 and 5.

[0061] As will be appreciated, automated sensor identificationprocedures may be readily implemented at monitors 20 a, 20 b. FIG. 3illustrates such functionalities. As shown, set-up for the procedureentails the interconnection of a sensor (e.g. sensor 10) to a monitor 20a, 20 b (step 200). In the applications of FIGS. 1A, 2A and 1B, 2B suchinterconnection requires the selective interconnection of connector end32 a, 32 b of cable 30 a, 30 b to port 22 a, 22 b ofphotoplethysmographic monitor 20 a, 20 b, respectively, and theinterconnection of a connector end 34 a, 34 b of cable 30 a, 30 b tosensor 10.

[0062] Following interconnection, the sensor identification proceduremay be initiated (step 202). Such sensor identification procedure may beautomatically initiated by monitor 20 a, 20 b upon electrical sensing ofone or more of the interconnections made in step 200 above.Alternatively, the sensor identification procedure may be initiated by auser via interface with user control panel 25 a, 25 b of monitor 20 a,20 b, e.g. upon prompting by display 24 a, 24 b of monitor 20 a, 20 b.In any case, monitor 20 a, 20 b may be pre-programmed so that the sensoridentification procedure must be completed or manually overridden by auser before photoplethysmographic measurements can proceed.

[0063] Upon initiation of the sensor identification procedure, sensoridentification module 40 a, 40 b may cause monitor 20 a, 20 b toautomatically apply a interrogation test signal to the interconnectedsensor (step 204) and correspondingly obtain a detector output signalfrom the sensor, such output defining a sensor “test signature”. Forexample, the test signature may indicate whether one or more lightsources comprising the interconnected sensor emitted light during one ormore time periods within a cycle of the interrogation test signal and/orthe intensity of any light emitted by one or more of the sources duringsuch time periods. Optionally, additional “test signatures” may beobtained by repeating the interrogation test signal cycle.

[0064] Upon obtainment of the test signature(s), processor 21 a, 21 b ofmonitor 20 a, 20 b may determine whether the test signature(s) is withina predetermined range of a “reference signature” (step 208) therebyindicating that a known, compatible sensor (e.g. sensor 10) isinterconnected to the monitor 20 a, 20 b. In the later regard, one ormore “reference signatures” may be stored at module 40 a or 40 b incorresponding preset relation to the expected performance of one or moresensors known to be compatible with the corresponding monitor 20 a or 20b. Where a plurality of sensors are compatible with monitor 20 a or 20b, a corresponding plurality of stored reference signatures may beemployed to identify the given interconnected sensor. If the sensor isidentified, monitors 21 a or 21 b may automatically provide forcontinuation of photoplethysmographic monitoring procedure (step 210),wherein one or more blood analyte concentration levels are determined byand monitors 20 a, 20 b (step 200). Alternatively, processors 21 a, 21 bmay provide for an output to a user (e.g. at display 24 a, 24 b)indicating that a compatible sensor (i.e., sensor 10) has been detectedand prompt the user to provide an input at user control panel 25 a toinitiate photoplethysmographic measurements procedures. In conjunctiontherewith, the blood analyte measurement module 28 a, 28 b may utilizestored values, or algorithms, selected/calibrated in correspondingrelation to the identified sensor, to make photoplethysmographicmeasurements the identification output value may be utilized to selectappropriate calibration values for sensor 10 (step 210).

[0065] In the event that the test signature obtained at step 208 isoutside of the predetermined range, processor 21 a, 21 b may bepre-programmed to disable monitor 20 a, 20 b from continuing to aphotoplethysmographic measurement procedure (step 214). Such disablementmay be accompanied by a corresponding output at display 24 a, 24 bindicating to the user that an inappropriate, or incompatible sensor hasbeen interconnected to the monitor 20 a, 20 b. Alternatively, a warningsignal may be output to a user at display 24 a, 24 b, whereuponprocessor 21 a, 21 b may be pre-programmed to allow a user to provide anoverride input at user control panel 25 a, 25 b to continuephotoplethysmographic measurement procedures (step 216). In anotherapproach, where the test signature obtained at step 208 is outside thepredetermined range, processor 21 a, 21 b may be preprogrammed to onlypartially disable monitor 20 a, 20 b from completing aphotoplethysmographic measurement procedure (step 214). For example,while certain performance-enhancing functionalities of processor 21 a,21 b may be disabled, other base measurement functionalities would notbe disabled.

[0066] Referring to FIG. 4, another embodiment of aphotoplethysmographic system is provided that is operable to obtainoutput signals from one or more of light sources 112, 114, and 116 inresponse to interrogation signal(s) applied thereto. As with the systemsdescribed above in conjunction with FIGS. 1 and 2, thephotoplethysmographic system includes a monitor 120 interconnected to asensor 110 via a cable 130. The photoplethysmographic monitor 120 mayinclude componentry similar or identical to photoplethysmographicmonitors 20 a and 20 b as discussed above, including a clock, processor,sensor identification module, blood analyte measurement module, lightsource drives, etc. Likewise, the photoplethysmographic monitor 120includes a port 122 having a plurality of electrical pins forinterconnection to corresponding sensor terminals 152-166, located onthe sensor 110.

[0067] As shown, the cable 130 utilizes eight lines, 182-196 tointerconnect the sensor terminals 152-156 on the sensor 110 to the pinswithin the port 122. In this regard, each sensor terminal 152-156 on thesensor may be interconnected to the monitor 120 using a dedicated line182-196. As may be appreciated, this allows for increased flexibility inapplying drive and/or interrogation signals from the monitor 120 to thesensor elements (i.e. light sources, detectors, etc.) within the sensor110.

[0068] The sensor 110 of FIG. 4 includes three light sources 112, 114,and 116 each interconnected between two of the four sensor terminals152-158. In particular, light sources 112, 114, and 116 are eachconnected between a unique pair of sensor terminals 152-158. Moreparticularly, each pair is a unique combination of two of the foursensor terminals 152-158, wherein each unique pair of terminals includesat least one terminal included in another pair of terminals. Inparticular, light source 112 is interconnected between sensor terminals154 and 156; light source 114 is interconnected between terminals 158and 154; and light source 116 is interconnected between sensor terminals152 and 158. The sensor further includes, a detector 118 interconnectedbetween sensors 160 and 162 and a bin resister 119 interconnectedbetween sensor terminals 164 and 166.

[0069] Interconnection of the light sources 112, 114, and 116 betweenthe four sensor terminals 152-156 allows interconnecting the lightsources 112, 114 and 116 to the monitor using four dedicated lines182-188. This four-terminal, three-light source arrangement allows forestablishing a unique circuit through each light source 112, 114 and116. For example, the monitor 120 may apply a positive charge to sensorterminal 152 and a negative terminal charge to sensor terminal 158 viacable lines 182 and 188, respectively, to apply a first drive orinterrogation signal to light source 116. Accordingly, a correspondingoutput signal may be produced across terminals 152 and 158. Dependingupon the electrical components included between each pair of sensorterminals 152-158, the polarity of the signal may be reversed as appliedto each pair of sensor terminals. Accordingly, a signal may be appliedwith two polarities to produce two output signals. By way of example,light source 116, which is reversed biased in one direction, may produceseparate outputs to a signal applied with two polarities. In thisregard, if light source 116 is an LED, it may produce a minimal andpredeterminable voltage drop across terminals 152 and 158 in response toa signal having a first polarity. Likewise, light source 116 may producean open circuit output signal in response to the same signal appliedhaving a second polarity. What is important is that each light source112, 114, and 116 may receive one or more drive and/or interrogationsignals from the monitor 120 allowing each light source 112, 114 and 116to be utilized for identification purposes and/or photoplethysmographicmeasurements. However, in the embodiment described herein below, one ofthe light sources 112, 114 and 116 is used only for identificationpurposes.

[0070]FIG. 5 illustrates a sensor identification process that may beimplemented with the photoplethysmographic system of FIG. 4. Initiallythe photoplethysmographic monitor 120 monitors (step 500) a firstcircuit to identify a continuity that indicates sensor connection. Thatis, photoplethysmographic monitor 120 continually monitors an initiallyopen circuit through lines 194, 196 of cable 130. Upon interconnection(step 510) of the sensor 110 to the cable 130, which is interconnectedto the photoplethysmographic monitor 120, bin resistor 119 is identifiedas being present across sensor terminals 164, 166. The bin resistor 119completes the monitored circuit through lines 194 and 196 providing acontinuity that indicates a sensor 110 has been interconnected (step510) to the photoplethysmographic monitor 120. As may be appreciated,this bin resister may also, in some instances, be utilized to provide anoutput signal (e.g., a predeterminable voltage drop) in response to themonitoring signal. Accordingly this output signal may be utilized forobtaining sensor information and/or for identification purposes.

[0071] In conjunction with completing the monitored circuit throughsensor terminals 164 and 166, interconnection (step 510) of the sensor110 to the cable 130 also connects (step 520) a plurality of terminalpairs 152-158; 154-158; 154-156 and 160-162 associated with sensorelements 116, 114, 112 and 118 to the monitor 120. That is, in additionto the circuit formed through the bin resistor 119, four individualcircuits are established using lines 182-192 of the cable 130. Each ofthose circuits may receive drive and/or interrogation signals from saidphotoplethysmographic monitor 120 for application across theirrespective sensor elements.

[0072] In response to the sensor 110 being interconnected (step 510) tothe monitor 120, a sensor identification procedure may be initiated(step 530). In this regard, the monitor 120 may perform and open andshort test through the terminal pairs 152-158; 154-158; 154-156 and160-162 to determine whether sensor elements are present. If one of thecircuits is open, the monitor may be disabled. Typically, the monitor120 will utilize one of the three light sources 112, 114, and 116 toperform a sensor identification procedure (step 530).

[0073] For the discussion herein, it will be assumed that light source116 is utilized for identification purposes, and light sources 112 and114 are utilized for photoplethysmographic monitoring purposes. However,it will be appreciated that other combinations may be utilized. In orderto utilize light source 116 as an identification element, the monitor120 may selectively apply (steps 540 a and 540 b) one or moreinterrogation signals to one of the terminals 152, 158 of light source116 in order to produce one or more output signals (steps 550 a and 550b) at the other terminal for use in sensor identification. In thisregard, the monitor 120 may apply a positive charge to sensor terminal152 and a negative terminal charge to sensor terminal 158 via cableconnection lines 182 and 188, respectively. Accordingly, passing theinterrogation signal through the light source 116 may cause apredeterminable change to the signal (i.e., an output signal) that maybe measured across sensor terminals 152, 158.

[0074] By way of example, passing a first interrogation signal throughthe light source 116 may result in a predeterminable minimal voltagedrop (e.g., not greater than an a known threshold value) acrossterminals 152 and 158. Accordingly, this known response may be used foridentification purposes. Alternatively, if a resistor were also beincorporated between terminals 152 and 158 (e.g., in series with lightsource 116; not shown) a predeterminable voltage drop having at least aminimum value may be produced across the terminals 152 and 158.

[0075] It will be noted that multiple interrogation signals may beapplied across sensor terminals 152 and 158 for application to lightsource 116. In this regard, interrogation signals having differentmagnitudes (i.e. voltage and/or current levels) may be applied (step540) across terminals 152 and 158 to obtain a plurality of outputs (step550) for use in sensor identification. Furthermore, in some instances,interrogation signals may be applied (step 540) to one or both of theother light sources 112, 114 to obtain (step 550) additional outputs.

[0076] In a preferred embodiment, at least two interrogation signalshaving different magnitudes are applied (step 540) to terminals 152 and158 to obtain (step 550) at least two output signals. Accordingly, theseoutput signals are utilized by the monitor 120 (e.g. an identificationmodule within the monitor) to identify the sensor 110 interconnected tothe monitor 120. That is, these output signals will be compared (step560) either individually or together to stored look-up values, or,processed to produce test signatures that will be compared (step 560) tostored lookup values. If the output signals/test signatures are within apredetermined range of the stored look-up values, the sensor 110 isdetermined to be compatible with the monitor 120 (i.e., the sensor isidentified) and the photoplethysmographic monitoring procedure continues(Step 580). Once the sensor 110 is identified, the circuit throughterminals 152 and 158 and identification element 116 may be deactivatedfrom further use. That is, to prevent interference during monitoring,light source 116 may be deactivated. In this regard, the identificationprocedure may be performed at a first time and photoplethysmographicmonitoring may be performed at a second subsequent time.

[0077] If the output value(s) are outside a predetermined allowablerange, the monitor 120 may be disabled or display a warning to a user(step 570). However, in one embodiment a manual override may be provided(step 575) allowing a user to provide an override input at a usercontrol panel, which may allow the monitor 120 to continue thephotoplethysmographic monitoring procedure (step 580).

[0078] Once the monitor 120 identifies the sensor 110, the outputsignals/test signature and/or sensor identification may be utilized toaccess stored values, or algorithms. That is, the monitor 120 may select(step 590) appropriate calibration information for use with the sensor110. Once properly calibrated, the monitor 120 may apply appropriatedrive signals via sensor terminals 154-156 and 154-158, to pulse lightsources 112 and 114, respectively. In conjunction with providing suchdrive signals to selectively pulse light sources 112 and 114, themonitor will also provide drive signals to the detector 118 viaterminals 160 and 162. As in the embodiments described above, thedetector 118 provides an output signal related to the light output ofthe pulsing light sources 112 and 114 as may be attenuated by patienttissue-under-test. Accordingly, the output of the detector 118 may beutilized to determine blood analyte values, such as SPO2, as well asphysiological parameters such as heart rate and/or respiration rates.

[0079] The embodiments described above are for exemplary purposes onlyand is not intended to limit the scope of the present invention. Variousadaptations, modifications and extensions of the describedsensor/system/method will be apparent-to those skilled in the art andare intended to be within the scope of the invention as defined by theclaims which follow. By way of example, different light sources 112, 114and 116 may be utilized for identification purposes by differentphotoplethysmographic monitors. In this regard, it will be appreciatedthat sensor 110 may be configured for use with multiplephotoplethysmographic monitors. Accordingly, different ones of thesemonitors may utilize different combinations of light sources 112, 114and 116 for identification and/or monitoring purposes.

What is claimed:
 1. A method using a photoplethysmographic system,comprising: releaseably interconnecting a photoplethysmographic sensorto a photoplethysmographic monitor, wherein a first pair of terminals onsaid sensor is connected for receiving first drive signals from saidmonitor for illuminating a first light source coupled between said firstpair of terminals, wherein a second pair of terminals on said sensor isconnected for receiving second drive signals from said monitor forilluminating a second light source coupled between said second pair ofterminals, wherein a third pair of terminals on said sensor is connectedfor receiving an interrogation signal from said monitor for applicationacross an identification element coupled between said third pair ofterminals, and wherein said first second and third connections eachutilize a unique combination of terminals and wherein each said firstsecond and third terminal pairs includes at least one terminal includedin another of said first second and third terminal pairs; applying aninterrogation signal across said third pair of terminals to obtain anoutput signal from said identification element; and utilizing saidoutput signal to identify said sensor.
 2. The method of claim 1, whereinapplying step comprises applying an electrical signal to one terminal ofsaid third pair of terminals to obtain said output signal at the otherterminal of said third pair of terminals.
 3. The method of claim 2,wherein said identification element is a diode.
 4. The method of claim3, wherein said output comprises a minimal and predeterminable voltagedrop across said diode.
 5. The method of claim 3, wherein said applyingstep further comprises; applying a first electrical signal to obtain afirst output signal from said diode; and applying a second electricalsignal to obtain a second output signal from said diode.
 6. The methodof claim 5, wherein said first and second electrical signals havedifferent magnitudes.
 7. The method of claim 6, wherein said first andsecond electrical signals have first and second current levels.
 8. Themethod of claim 7, wherein said first and second current level areselected to produce first and second minimal and predeterminable voltagedrops across said diode.
 9. The method of claim 8, wherein said firstand second voltage drops are substantially equal.
 10. The method ofclaim 7, wherein said first and second electrical signals have apositive polarity and a negative polarity, respectively, as applied tosaid identification element.
 11. The method of claim 1, furthercomprising: upon obtaining said output signal, disabling said third pairof terminals on said sensor.
 12. The method of claim 1, furthercomprising: applying an interrogation signal across at least one of saidfirst and second pairs of terminals to obtain an additional outputsignal from at least one of said first and second light sources.
 13. Themethod of claim 1, further comprising: establishing a connection with afourth pair terminals on said sensor operable to complete a circuitmonitored by said monitor to identify sensor interconnection.
 14. Themethod of claim 13, further comprising: applying an electrical signal toone terminal of said fourth pair of terminals to obtain aninterconnection output signal at the other terminal of said fourth pairof terminals
 15. The method of claim 14, further comprising: uponidentifying said interconnection output signal, performing said applyingstep across said third pair of terminals on said sensor.
 16. The methodof claim 14, wherein said interconnection output signal is utilizedprocure sensor information.
 17. The method of claim 1, upon identifyingsaid sensor, further comprising the step of: applying predetermineddrive signals to one terminal of at least one of said first and secondterminal pairs on said sensor for controllably illuminating at least oneof said first and second light sources.
 18. The method of claim 17,wherein said at least one of said first and second light sourcesilluminates patient tissue-under-test.
 19. The method of claim 18,further comprising: establishing a connection with a fifth pair ofterminals on said sensor having a light detector coupled there between;and applying a detector drive signal to one terminal of said fifth pairof terminals to obtain a detector output signal at the other terminal ofsaid third pair of terminals, wherein said detector output signal isindicative of light absorption of said tissue-under-test.
 20. The methodof claim 15, wherein said detector output signal is utilized for atleast one of: determining a blood analyte concentration value; anddetermining at least one physiological parameter.
 21. The method ofclaim 20, wherein said blood analyte concentration value comprises ablood oxygen value.
 22. The method of claim 20, wherein saidphysiological parameter comprises a heart rate.
 23. The method of claim1, wherein releaseably interconnecting further comprises:interconnecting each terminal on said sensor to said monitor via adedicated electrical pathway.
 24. The method of claim 23, wherein fourdedicated electrical pathways interconnect said first, second and thirdpairs of terminals on said sensor to said monitor.
 25. The method ofclaim 1, further comprising: comparing said output signal to apredetermined range of values to select information for use incalibrating said monitor.
 26. The method of claim 25, wherein when saidoutput signal is outside said predetermined range, said method furthercomprising at least one of: providing an output to a user indicatingthat the sensor is not compatible with said monitor; and disabling saidmonitor for use with said interconnected sensor.
 27. The method of claim25, wherein when said output signal is within said predetermined range,said method further comprising: utilizing said output signal to selectone of a plurality of calibration values for use inphotoplethysmographic monitoring.
 28. A photoplethysmographic monitoringsystem, comprising: a photoplethysmographic sensor including: a firstlight source interconnected between a first pair of sensor terminals; asecond light source interconnected between a second pair of sensorterminals; and an identification element interconnected between a thirdpair of sensor terminals, wherein each of said pairs of sensor terminalscomprises a unique combination of sensor terminals and wherein each saidfirst second and third pairs of sensor terminals includes at least oneterminal included in another of said first second and third pairs ofsensor terminals; a photoplethysmographic monitor removeablyinterconnectable to each of said first, second and third pairs of sensorterminals, said monitor operative to selectively apply predeterminedsignals to a first terminal of each of said pairs of sensor terminalsand obtain an output signal at a second terminal of each of said pairsof sensor terminals; and a processor operatively associated with saidmonitor operative to utilize at least one said output signal to identifysaid sensor.
 29. The system of claim 28, wherein said first, second andthird pairs of terminals each comprise a unique combination of two offour terminals on said sensor.
 30. The system of claim 29, wherein saidfour terminals are removeably interconnected to said monitor via fourdedicated electrical pathways.
 31. The system of claim 28, wherein saidmonitor is operative to apply an interrogation signal across said thirdpair of sensor terminals to obtain an identification output signal fromsaid identification element.
 32. The system of claim 31, wherein saididentification element comprises a diode.
 33. The system of claim 32,wherein said diode produces a minimal and predeterminable voltage dropacross said third pair of terminals in response to said interrogationsignal.
 34. The system of claim 31, wherein said monitor is operative toapply first and second interrogation signals across said third pair ofsensor terminals to obtain first and second identification outputsignals from said identification element.
 35. The system of claim 34,wherein said first and second interrogation signals having differentmagnitudes.
 36. The system of claim 35, wherein said first and secondinterrogation signals have different current levels.
 37. The system ofclaim 36, wherein said identification element is a diode and said firstand second output signals comprise first and second minimal andpredeterminable voltage drops across said third pair of terminals. 38.The system of claim 37, wherein said diode is selected such that saidfirst and second voltage drops are substantially equal.
 39. The systemof claim 28, wherein said monitor is operative to apply interrogationsignals to at least one of said first and second pairs of sensorterminals to obtain at least one identification output from one of saidfirst and second light sources.
 40. The system of claim 28, wherein,upon identifying said sensor, said monitor is operative to deactivatesaid connection with said third pair of sensor terminals.
 41. The systemof claim 28, wherein said sensor further comprises: a light detectorinterconnected between a fourth pair of sensor terminals for detectinglight output signals from said first and second light sources andproviding a detector output signal indicative thereof.
 42. The system ofclaim 42, wherein said processor is operative to utilize said detectoroutput signal to compute at least one blood analyte concentration value.43. The system of claim 28, further comprising: a cable interconnectingsaid sensor to said monitor, wherein said cable provides a dedicatedelectrical pathway between each said sensor terminal and said monitor.